feat: vendor bodgit/sevenzip package to remove go4.org dependency

Vendored the sevenzip package to eliminate dependency chain:
- sevenzip -> go4.org -> 25+ Google/Cloud/telemetry packages

Changes:
- Added internal/sevenzip/ with full package source
- Inlined go4.org/readerutil into multireaderat.go
- Updated all internal imports to use bookhoard/internal/sevenzip
- Preserved .cb7 comic archive support

This reduces bloat by ~4.9 MB and removes unused telemetry
dependencies while maintaining all functionality.

internal/sevenzip/register.go

@@ -0,0 +1,92 @@
+package sevenzip
+
+import (
+	"errors"
+	"io"
+	"sync"
+
+	"bookhoard/internal/sevenzip/internal/aes7z"
+	"bookhoard/internal/sevenzip/internal/bcj2"
+	"bookhoard/internal/sevenzip/internal/bra"
+	"bookhoard/internal/sevenzip/internal/brotli"
+	"bookhoard/internal/sevenzip/internal/bzip2"
+	"bookhoard/internal/sevenzip/internal/deflate"
+	"bookhoard/internal/sevenzip/internal/delta"
+	"bookhoard/internal/sevenzip/internal/lz4"
+	"bookhoard/internal/sevenzip/internal/lzma"
+	"bookhoard/internal/sevenzip/internal/lzma2"
+	"bookhoard/internal/sevenzip/internal/zstd"
+)
+
+// Decompressor describes the function signature that decompression/decryption
+// methods must implement to return a new instance of themselves. They are
+// passed any property bytes, the size of the stream and a slice of at least
+// one io.ReadCloser's providing the stream(s) of bytes.
+type Decompressor func([]byte, uint64, []io.ReadCloser) (io.ReadCloser, error)
+
+var (
+	//nolint:gochecknoglobals
+	decompressors sync.Map
+
+	errNeedOneReader = errors.New("copy: need exactly one reader")
+)
+
+func newCopyReader(_ []byte, _ uint64, readers []io.ReadCloser) (io.ReadCloser, error) {
+	if len(readers) != 1 {
+		return nil, errNeedOneReader
+	}
+	// just return the passed io.ReadCloser)
+	return readers[0], nil
+}
+
+//nolint:gochecknoinits
+func init() {
+	// Copy
+	RegisterDecompressor([]byte{0x00}, Decompressor(newCopyReader))
+	// Delta
+	RegisterDecompressor([]byte{0x03}, Decompressor(delta.NewReader))
+	// LZMA
+	RegisterDecompressor([]byte{0x03, 0x01, 0x01}, Decompressor(lzma.NewReader))
+	// BCJ
+	RegisterDecompressor([]byte{0x03, 0x03, 0x01, 0x03}, Decompressor(bra.NewBCJReader))
+	// BCJ2
+	RegisterDecompressor([]byte{0x03, 0x03, 0x01, 0x1b}, Decompressor(bcj2.NewReader))
+	// PPC
+	RegisterDecompressor([]byte{0x03, 0x03, 0x02, 0x05}, Decompressor(bra.NewPPCReader))
+	// ARM
+	RegisterDecompressor([]byte{0x03, 0x03, 0x05, 0x01}, Decompressor(bra.NewARMReader))
+	// SPARC
+	RegisterDecompressor([]byte{0x03, 0x03, 0x08, 0x05}, Decompressor(bra.NewSPARCReader))
+	// Deflate
+	RegisterDecompressor([]byte{0x04, 0x01, 0x08}, Decompressor(deflate.NewReader))
+	// Bzip2
+	RegisterDecompressor([]byte{0x04, 0x02, 0x02}, Decompressor(bzip2.NewReader))
+	// Zstandard
+	RegisterDecompressor([]byte{0x04, 0xf7, 0x11, 0x01}, Decompressor(zstd.NewReader))
+	// Brotli
+	RegisterDecompressor([]byte{0x04, 0xf7, 0x11, 0x02}, Decompressor(brotli.NewReader))
+	// LZ4
+	RegisterDecompressor([]byte{0x04, 0xf7, 0x11, 0x04}, Decompressor(lz4.NewReader))
+	// AES-CBC-256 & SHA-256
+	RegisterDecompressor([]byte{0x06, 0xf1, 0x07, 0x01}, Decompressor(aes7z.NewReader))
+	// LZMA2
+	RegisterDecompressor([]byte{0x21}, Decompressor(lzma2.NewReader))
+}
+
+// RegisterDecompressor allows custom decompressors for a specified method ID.
+func RegisterDecompressor(method []byte, dcomp Decompressor) {
+	decompressors.Store(string(method), dcomp)
+}
+
+func decompressor(method []byte) Decompressor {
+	di, ok := decompressors.Load(string(method))
+	if !ok {
+		return nil
+	}
+
+	if d, ok := di.(Decompressor); ok {
+		return d
+	}
+
+	return nil
+}